Highly effective gas barriers are required for containers and packaging of food products, toiletry products, drugs, medical supplies, electronic members etc., for protecting the contents. Most currently used gas barriers are things manufactured from chlorine based materials such as polyvinylidene chloride, and things manufactured by evaporating inorganic material, so that they emit enormous amounts of carbon dioxide and heat at manufacturing or disposing. Furthermore, chlorine-based materials have a problem in that dioxin is generated from them, and evaporated inorganic films have some problems in that they can damage an incinerator on burning, removal of the film is required for recycling, and so on. Therefore, gas barrier materials are desired to be converted to eco-friendly materials capable of preventing these problems.
A noteworthy eco-friendly material is cellulose. Cellulose is contained in cell walls of plants, secretion from microbes, mantles of sea squirts, etc., is the most common polysaccharide on earth, has biodegradability, high crystallinity, excellent stability and safety. Therefore, applying it to various fields is expected.
Cellulose is nearly insoluble in water and general solvent, because cellulose has strong intramolecular hydrogen bonds and high crystallinity. Therefore, studies on the improvement of the resolvability are made actively. Among them, a method where only the primary hydroxyl group at the C6 position among three hydroxyl groups which cellulose has is oxidized with TEMPO catalyst, and converted to a carboxyl group through an aldehyde group or a ketone group, is capable of oxidizing only the primary hydroxyl group selectively and performing the reaction under relatively mild conditions such as aqueous condition or room temperature. Therefore, this method attracted much attention recently. Furthermore, it is known that performing TEMPO oxidation with natural cellulose allows only the nano-order crystal surface to be oxidized keeping the crystallinity of cellulose, then only performing a slight mechanical process allow fine celluloses to water-disperse. In addition, a film formed by drying the water-dispersed fine celluloses is highly gas impermeable due to its fine structure and high crystallinity.
PTL1 discloses a gas barrier composite form which has a gas barrier layer on a base material, the gas barrier layer containing fine cellulose fibers.
PTL2 discloses that forming a fine cellulose fiber layer on a base material, furthermore forming a hydrophobizing material layer on them, and repeating these steps additionally once, twice or more allows a laminate to have a moisture barrier property.